Most microbial infections in the body are caused by bacteria growing in biofilms composed of single or multiple bacterial species. Biofilms are typically matrix-enclosed microbial aggregates associated with each other and a solid surface. Bacteria within biofilms have an increased resistance to antimicrobial agents relative to that of planktonic cells of the same species. The relative impermeability of biofilms to compounds such as antimicrobial agents may be one reason why microbial infections associated with biofilms are difficult to treat.